1. Field of the Invention
The invention relates to an electrophotographic photosensitive drum supporting apparatus for rotatably supporting an electrophotographic photosensitive drum (hereinafter referred to as the “photosensitive drum”), a process cartridge using the electrophotographic photosensitive drum and the supporting apparatus, and an electrophotographic image forming apparatus.
Here, the electrophotographic image forming apparatus is an apparatus for forming an image on a recording medium (e.g., paper or an OHP sheet) by the use of an electrophotographic image forming process. Examples of the electrophotographic image forming apparatus include, for example, an electrophotographic copying machine, an electrophotographic printer (such as a laser beam printer or an LED printer) and a word processor.
Also, the process cartridge refers to at least one of charging means, developing means and cleaning means as process means and a photosensitive drum integrally made into a cartridge which is made detachably mountable on a main body of an electrophotographic image forming apparatus.
2. Description of the Related Art
Heretofore, a process cartridge system has been adopted in the electrophotographic image forming apparatus.
According to this cartridge system, the maintenance of the apparatus can be effected by a user himself without resort to a serviceman. Consequently, operability could be improved. So, this cartridge system is widely used in electrophotographic image forming apparatus.
In recent years, demand for a color electrophotographic image forming apparatus which can effect the forming of a color image has increased.
The color electrophotographic image forming apparatus effects the forming of images of four colors independently of one another. Therefore, the positional deviation of an image-formed point at which an image is formed by each photosensitive drum from a target (ideal) position appears as color misregistration between respective colors in the image.
As a countermeasure for this, there is, for example, a controlling method of measuring the position of the image formed point of each color, and correcting the position. Also, there is a method of disposing a rotary encoder or the like for measuring rotation fluctuation on a drum driving shaft, and controlling a driving motor.
Also, the shape of a bearing for supporting the photosensitive drum is made into a substantially V-shape. There is also conceived a construction for reducing the backlash of the photosensitive drum in the radial direction thereof. In this construction, however, new biasing means is added to the V-shaped portion to bias the photosensitive drum (Japanese Patent Application Laid-Open No. H10-186758 (FIGS. 4 and 5)).
Recently, the downsizing and lower costs of the process cartridge and the electrophotographic image forming apparatus have come to be further demanded. For that purpose, it is necessary to adopt a part construction making the downsizing possible, and decreasing the number of parts. On the other hand, even if the number of parts is decreased, an improvement in the quality of image and the downsizing and lower cost of the apparatus must be produced.